Protective immune responses induced by vaccination against influenza viruses are primarily directed to the viral HA protein, which is a glycoprotein on the surface of the virus responsible for interaction of the virus with host cell receptors. HA proteins on the virus surface are trimers of HA protein monomers that are enzymatically cleaved to yield amino-terminal HA1 and carboxy-terminal HA2 polypeptides. The globular head consists exclusively of the major portion of the HA1 polypeptide, whereas the stem that anchors the HA protein into the viral lipid envelope is comprised of HA2 and part of HA1. The globular head of a HA protein includes two domains: the receptor binding domain (RBD), an ˜148-amino acid residue domain that includes the sialic acid-binding site, and the vestigial esterase domain, a smaller ˜75-amino acid residue region just below the RBD. The globular head includes several antigenic sites that include immunodominant epitopes. Examples include the Sa, Sb, Ca1, Ca2 and Cb antigenic sites (see, for example, Caton A J et al, 1982, Cell 31, 417-427). The RBD-A region includes the Sa antigenic site and part of the Sb antigenic site.
Antibodies against influenza often target variable antigenic sites in the globular head of HA, which surround a conserved sialic acid binding site, and thus, neutralize only antigenically closely related viruses. The variability of the HA head is due to the constant antigenic drift of influenza viruses and is responsible for seasonal endemics of influenza. In contrast, the HA stem is highly conserved and experiences little antigenic drift. Unfortunately, unlike the immunodominant head, the conserved HA stem is not very immunogenic. Furthermore, gene segments of the viral genome can undergo reassortment (antigenic shift) in host species, creating new viruses with altered antigenicity that are capable of becoming pandemics [Salomon, R. et al. Cell 136, 402-410 (2009)]. Until now, each year, influenza vaccine is updated to reflect the predicted HA and neuraminidase (NA) for upcoming circulating viruses.
Recently, an entirely new class of broadly neutralizing antibodies against influenza viruses was isolated that recognize the highly conserved HA stem [Corti, D. et al. J Clin Invest 120, 1663-1673 (2010); Ekiert, D. C. et al. Science 324, 246-251 (2009); Kashyap, A. K. et al. Proc Natl Acad Sci USA 105, 5986-5991 (2008); Okuno, Y. et al. J Virol 67, 2552-2558 (1993); Sui, J. et al. Nat Struct Mol Biol 16, 265-273 (2009); Ekiert, D. C. et al. Science 333, 843-850 (2011); Corti, D. et al. Science 333, 850-856 (2011)]. Unlike strain-specific antibodies, those antibodies are capable of neutralizing multiple antigenically distinct viruses, and hence inducing such antibodies has been a focus of next generation universal vaccine development [Nabel, G. J. et al. Nat Med 16, 1389-1391 (2010)]. However, robustly eliciting these antibodies with such heterologous neutralizing profile by vaccination has been difficult [Steel, J. et al. MBio 1, e0018 (2010); Wang, T. T. et al. PLoS Pathog 6, e1000796 (2010); Wei, C. J. et al. Science 329, 1060-1064 (2010)]. Removal of the immunodominant head region of HA (which contains competing epitopes) and stabilization of the resulting stem domain through genetic manipulation is one potential way to improve the elicitation of these broadly neutralizing stem antibodies.
Current vaccine strategies for influenza use either a chemically inactivated or a live attenuated influenza virus. Both vaccines are generally produced in embryonated eggs which present major manufacturing limitations due to the time consuming process and limited production capacity. Another more critical limitation of current vaccines is its highly strain-specific efficacy. These challenges became glaring obvious during emergence of the 2009 H1N1 pandemic, thus validating the necessity for new vaccine platforms capable of overcoming these limitations. Virus-like particles represent one of such alternative approaches and are currently being evaluated in clinical trials [Roldao, A. et al. Expert Rev Vaccines 9, 1149-1176 (2010); Sheridan, C. Nat Biotechnol 27, 489-491 (2009)]. Instead of embryonated eggs, VLPs that often comprise HA, NA and matrix protein 1 (M1) can be mass-produced in mammalian or insect cell expression systems [Haynes, J. R. Expert Rev Vaccines 8, 435-445 (2009)]. The advantages of this approach are its particulate, multivalent nature and the authentic display of properly folded, trimeric HA spikes that faithfully mimic the infectious virion. In contrast, by the nature of its assembly, the enveloped VLPs contain a small but finite host cell component that may present potential safety, immunogenicity challenges following repeated use of this platform [Wu, C. Y. et al. PLoS One 5, e9784 (2010)]. Moreover, the immunity induced by the VLPs is essentially the same as current vaccines, and thus, will not likely significantly improve both potency and breadth of vaccine-induced protective immunity. In addition to VLPs, a recombinant HA protein has also been evaluated in humans [Treanor, J. J. et al. Vaccine 19, 1732-1737 (2001); Treanor, J. J. JAMA 297, 1577-1582 (2007)], though the ability to induce protective neutralizing antibody titers are limited. The recombinant HA proteins used in those trials were produced in insect cells and might not form native trimer preferentially [Stevens, J. Science 303, 1866-1870 (2004)].
Despite several alternatives to conventional influenza vaccines, advances in biotechnology in past decades have allowed engineering of biological materials to be exploited for the generation of novel vaccine platforms. Ferritin, an iron storage protein found in almost all living organisms, is an example which has been extensively studied and engineered for a number of potential biochemical/biomedical purposes [Iwahori, K. U.S. Patent 2009/0233377 (2009); Meldrum, F. C. et al. Science 257, 522-523 (1992); Naitou, M. et al. U.S. Patent 2011/0038025 (2011); Yamashita, I. Biochim Biophys Acta 1800, 846-857 (2010)], including a potential vaccine platform for displaying exogenous epitope peptides [Carter, D. C. et al. U.S. Patent 2006/0251679 (2006); Li, C. Q. et al. Industrial Biotechnol 2, 143-147 (2006)]. Its use as a vaccine platform is particularly interesting because of its self-assembly and multivalent presentation of antigen which induces stronger B cell responses than monovalent form as well as induce T-cell independent antibody responses [Bachmann, M. F. et al. Annu Rev Immunol 15, 235-270 (1997); Dintzis, H. M. et al. Proc Natl Acad Sci USA 73, 3671-3675 (1976)]. Further, the molecular architecture of ferritin, which consists of 24 subunits assembling into an octahedral cage with 432 symmetry has the potential to display multimeric antigens on its surface.
There remains a need for an efficacious influenza vaccine that provides robust protection against influenza virus. There particularly remains a need for an influenza vaccine that protects individuals from heterologous strains of influenza virus, including evolving seasonal and pandemic influenza virus strains of the future. The present invention meets this need by providing a novel nanoparticle-based vaccine consisting of a novel HA stabilized stem (SS) without the variable immunodominant head region genetically fused to the surface of nanoparticles (gen6 HA-SS np) resulting in an influenza vaccine that is easily manufactured, potent, and elicits antibodies that are broadly heterosubtypic protective.